Toilets which cannot be connected to sewer mains or sewage treatment equipment usually have storage tanks which hold the accumulated waste until such time as it is convenient to pump the waste into a tanker truck for transport to another location where sewage processing is available. This is a common procedure for mobile toilets as for example toilets installed in commercial airliners. Airliner toilets flush by using recirculated chemically treated waste water or by using a small amount of fresh water assisted by the pull of a vacuum. The waste is either stored in tanks beneath each toilet or in remote tanks which hold the waste from several toilets. These tanks can be accessed through connections in the service panels underneath the plane. When the plane is serviced the waste water is drained or pumped into a tanker truck connected at the service panels.
The weight of water used to flush toilets and the weight of the associated tanks and pipes is undesirable in an aircraft since it reduces the available payload. The weight of water used in each recirculating airline toilet is approximately 68 kg. The weight of water required to operate a vacuum toilet during a long flight is approximately 41 kg. A dry toilet which `flushes` using a thin bowl liner film as described in International Application No. PCT/US95/03004 uses no water but instead uses 5 grams of plastic film per flush or approximately 0.6 kg during a long flight. In an airliner with ten toilets this could result in an approximate weight saving of 400 to 700 kg. There would also be additional weight savings from the elimination of equipment required to handle and store waste water.
The weight saving advantage of a dry toilet is offset by the difficulty of removing the toilet waste conveniently from positions outside the plane. The dry toilet waste combined with plastic film will not ordinarily flow through pipes to the service panel locations. In the absence of flushing water the film as well as other solid waste will cling to the walls of a pipe and will not be easily dislodged by gravity or by airflow.